A conventional pulse sensor for detecting a pulse wave of a living body based on a light receiving signal of light, which is transmitted through the living body when the living body is emitted with light from a light emitting unit, has been known. In such a pulse wave sensor, since an intensity of the received light varies with a pulsation of the living body, pulse wave information (e.g., a heart rate of the living body, etc.) can be obtained based on characteristics of the pulse wave signal (e.g., a fluctuation cycle of the pulse wave signal, etc.) corresponding to the intensity of the received light.
An amplitude of the pulse wave signal depends on a light emission intensity of the light emitting unit. However, if the amplitude of the pulse wave signal becomes too small as the light emission intensity is small, it may become difficult to obtain accurate pulse wave information. On the other hand, if the light emission intensity becomes too large in order to increase the amplitude of the pulse wave signal, it may also become difficult to obtain accurate pulse wave information due to saturation of the pulse wave signal. Thus, in order to obtain the accurate pulse wave information, it is necessary to optimize the amplitude of the pulse wave signal. If there are no individual differences in attenuations (i.e., light absorbances) of light in living bodies, the light emission intensity required to obtain proper amplitude of the pulse wave signal is uniquely determined. However, there may be differences among attenuations of individuals. In addition, an attenuation may vary each time for the same person depending on how to install the pulse wave sensor, etc.
A following amplitude detection method may be considered as one of methods for optimizing an amplitude of a pulse wave signal. The amplitude detection method includes directly reading amplitudes of the pulse wave signal (i.e., a difference between the maximum signal value and the minimum signal value) by emitting light with a test light emission intensity from a light emitting unit before an actual detection period during which a pulse wave is actually detected, and then setting a light emission intensity in the actual detection period (i.e., a normal light emission intensity) based on the read amplitudes. If the cycle of pulse wave is 1 Hz, in order to directly read an amplitude of the pulse wave signal with a single test light emission intensity, it takes at least one second, generally two to three seconds to ensure some degrees of accuracy. In addition, in order to provide a high-accurate setting of the light emission intensity (i.e., the normal light emission intensity) in the actual detection period, directly sequentially reading amplitudes of the pulse wave signal (i.e., a difference between the maximum signal value and the minimum signal value) by sequentially emitting light with a plurality of different test light emission intensities from light emitting unit, and then setting the light emission intensity in the actual detection period (i.e., the normal light emission intensity) based on the plurality of read amplitudes may be also contemplated. In this case, a required time may be equal to “(the number of types of test light emission intensities)×2” through “(the number of types of test light emission intensities)×3.”
When an adjustment process for amplitude optimization is performed, i.e., when an adjustment process for optimization of light emission intensity is performed, actual pulse wave detection is not performed. Thus, a shorter time required for the adjustment process is better.